Drill Bit with Angulary Offset Centerlines

ABSTRACT

A drill bit for use in horizontal directional drilling. In a preferred embodiment the drill bit has a connector section having a first axis of rotation. The connector section is used to connect the drill bit to a beacon housing for thrust and rotation therewith. A bit body is disposed next to the connector section and slopes from the connector section to a front nose section. The front nose section has a frontwardly facing surface that supports a plurality of cutting teeth. The front nose section and the bit body comprise a second axis of rotation about which the front nose section and the bit body are rotated. The first axis of rotation and the second axis of rotation are angularly offset at an offset angle of between four degrees and ten degrees.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of U.S. Provisional Patent Application No. 61/332,633, filed May 7, 2010, the contents of which are incorporated fully herein by reference.

FIELD OF THE INVENTION

The present invention relates in general to horizontal directional drilling (“HDD”) drill bits and in particular to an offset rock bit.

SUMMARY OF THE INVENTION

The invention is directed to a drilling bit for use in directional drilling. The bit comprises a connector section having a first axis of rotation, a front nose section, and a bit body. The front nose section has a frontwardly facing surface. The bit body slopes from the connector section to the front nose section. The front nose section and the bit body comprise a second axis of rotation about which the front nose section and bit body are rotated. The first axis of rotation and the second axis of rotation are angularly offset at an offset angle of between four degrees and ten degrees.

The present invention is also directed to a horizontal directional drilling system. The system comprises a drive machine, a drill string, and a downhole tool assembly. The drill string is connected to the drive machine and operable in response to rotation and thrust forces from the drive machine. The downhole tool assembly is connected to a downhole end of the drill string. The downhole tool assembly comprises a beacon assembly and a drill bit. The drill bit comprises a connector section, a front nose section and a bit body. The connector section has a first axis of rotation. The front nose section has a frontwardly facing surface. The bit body slopes from the connector section to the front nose section. The front nose section and the bit body comprise a second axis of rotation about which the front nose section and bit body are rotated. The first axis of rotation and the second axis of rotation are angularly offset at an offset angle of between four degrees and ten degrees.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a horizontal directional drilling system for drilling a horizontal borehole in accordance with the present invention.

FIG. 2 is a side view of a downhole tool assembly for use in accordance with the present invention. FIG. 2 shows the beacon housing and drill bit of the present invention.

FIG. 3 is a diagrammatic illustration of the drill bit shown in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to the drawings in general and FIG. 1 in particular, there is shown therein a horizontal directional drilling machine 10 constructed in accordance with the present invention. FIG. 1 illustrates the usefulness of horizontal directional drilling by demonstrating that a borehole 12 can be made without disturbing an above-ground structure, namely the roadway as denoted by reference numeral 14. FIG. 1 also illustrates the present invention by showing the use of a downhole tool 16, comprising a drill bit 18, operatively connected to a drill string 20 and adapted to cut through hard soil or rock formations.

Referring still to FIG. 1, the HDD machine 10 generally comprises a frame 22, for supporting a rotary drive machine 24, and an earth anchor 26. The rotary drive machine 24 is movably supported on the frame 22 between a first position and a second position. Movement of the rotary drive machine 24, by way of an axial advancement means (not shown), between the first position and the second position axially advances the drill string 20, downhole tool 16, and drill bit 18 through the ground.

The drill string 20 is operatively connected to the rotary drive machine 24 at one end and the downhole tool 16 at the other end. In the present invention the drill string 20 may comprise a series of pipe segments that transmit torque and thrust to the drill bit 18.

The HDD system of FIG. 1 may also comprise an above-ground tracking system 30 used to track the location of the downhole tool 16 as it moves through the ground. Such tracking systems 30 are capable of determining the location, depth, and orientation (pitch, roll, and yaw) of the downhole tool. Orientation and location information from the tracking system is provided to the drive system's operator to assist the operator in guiding the downhole tool 16 through the ground.

The need to effectively and accurately steer the downhole tool 16 has resulted in the development of many different “steerable” drill bits. One such steerable drill bit is an angled or slant faced drill bit. In order to steer the drill bit, the operator positions the bit with the angled face pointed in the direction of the desired turn and begins to rock the drill string and downhole tool through less than 360 degrees of rotation to cut away material from a face of the borehole to cut a relief in the side of the borehole in which the operator wants to steer. The downhole tool 16 is also pushed into the relief until it is large enough to change the direction of the downhole tool and the borehole. This steering method may be used to steer the tool in any direction. To drill in a straight line, the steerable drill bit 18 is rotated about the full 360 degrees, usually clockwise, while it is thrust forward by the rotary drive machine 24.

Turning now to FIG. 2 there is shown therein a downhole tool 16 of the present invention. The downhole tool 16 comprises a beacon assembly 28 and the drill bit 18. The beacon assembly 28 is generally comprised of a cylindrical housing 32. The housing 32 may have a drill bit connector 34 at one end and a drill string connector 36 at the other end. As shown in FIG. 2 the drill bit connector 34 may comprise a set of female threads matched to a set of male threads 38 on the drill bit 18. However, one skilled in the art will appreciate that alternative types of connections may be made without departing from the spirit of the invention. For example, the Splinelok® connection sold by Earth Tool LLC may be used to connect the housing 32 to the drill bit 18. Likewise, the drill string connector 36 may comprise a threaded connection or any other connection method used in the HDD industry. One skilled in the art will also appreciate that a bent sub (not shown) may be connected to the drill string connector 36 between the housing 32 and the terminal end of the drill string 20 (FIG. 1) to offset the downhole tool 16 from the central axis of the drill string 20 (FIG. 1) to provide enhanced steering capabilities.

Continuing with FIG. 2, the cylindrical housing 32 is generally elongate and composed of a resilient material such as stainless steel. The housing 32 may comprise an elongate cavity 40 within which an array of downhole electronics may be supported. The downhole electronics may comprise a beacon 42. A locating slot 44 may be positioned on a sidewall of the cavity 40 and used to “clock” the beacon 42 at a desired orientation relative to the drill bit 18. The housing 32 may have a window 46 through which the beacon 42 may be placed into the housing. A door 48 may then be secured to the housing 32 with a bolt 50 to cover the window 46. Alternatively, the beacon 42 may be loaded into the housing 32 from either end. An acceptable end-loading housing and locating slot are described in co-owned and co-pending U.S. patent application Ser. No. 13/085,220.

The beacon 42 may comprise an electromagnetic transmitting antenna (not shown) and a set of orientation sensors (not shown) used to detect the orientation of the downhole tool assembly 16. The beacon may likewise include a temperature sensor and a power level sensor to measure remaining battery life. Information from the various sensors may be embedded onto the signal transmitted by the antenna to communicate such information to the above-ground receiver 30. The receiver 30 is capable of decoding the signal to receive the operational and orientation information contained thereon and capable of measuring the strength of the signal to determine the distance between the receiver and the downhole tool 16.

Referring still to FIG. 2, the drill bit 18 comprises a connector section 52, a front nose section 54, and a bit body 56 which slopes from the connector section to the front nose section. The connector section 52 has a first axis of rotation 58 about which the connector section is rotated. The first axis of rotation 58 may be collinear with a centerline of the connector section 52. The front nose section 54 has a frontwardly facing surface 60. The front nose section 54 and the bit body 56 comprise a second axis of rotation 62 about which the front nose section and the bit body are rotated. The first axis of rotation 58 and the second axis of rotation are angularly offset at an offset angle of between four (4) degrees and ten (10) degrees. Preferably the first axis of rotation 58 and the second axis of rotation 62 are angularly offset at an offset of six (6) degrees.

The connector section 52, as discussed above, may comprise a threaded portion 38 for connecting the drill bit 18 to the housing 32. The connector section 52 may also comprises a fluid path 66. The fluid path 66 provides a pathway for drilling fluid to pass through the drill hit and out of fluid ejection ports (not shown) spaced about the surface of the bit 18.

As shown in FIG. 2, the connector section 52 may transition to the bit body 56 in a bit having a unibody construction. However, one skilled in the art will appreciate that the connector section 52 and the bit body may be fabricated as separate parts and joined by either a connection joint or by welding. In a unibody embodiment the raw material is turned about the first axis of rotation 58 to cut the threads 38 and the outer periphery of the connector section 52. Once the machining of the connector section 52 has been completed, the raw material is repositioned to cut the bit body 56 and the nose section 54 at an offset angle to the first axis of rotation 58. The raw material is turned about the second axis of rotation 62 to form the bit body 56 and nose section 54.

The bit body 56 may comprise a steering face 68 having a rise over run ratio of between 2:1 and 4:1. A preferable steering face will have a rise over run ratio of 3:1. The steering face 68 engages the front face of the borehole and deflects the nose section 54 in a desired steering direction. The offset angle between the first axis of rotation and the second axis of rotation raises the steering face 68 into a position that allows cutting teeth 70 to engage the face of the borehole in the desired steering direction in a more aggressive manner than traditional directional drill bits. This feature provides more immediate control of the steer as well as a sharper turn radius.

Turning now to FIG. 3, the drill bit 18 of the present invention is shown in greater detail. The connector section 52, comprising male threads 38, is shown formed along the first axis of rotation 58. The connector section 52 is connected to the housing 32 and drill string 20 (FIG. 1) for rotation therewith. Thus, the first axis of rotation 58 may be collinear with the central axis of rotation of the housing 32 (FIG. 2) and the axis of rotation of the drill string.

The bit body 56 is shown having angled steering face 68, and a deflection surface 72. The deflection surface 72 is formed from a resilient material and is generally welded about a portion of the circumference of the bit body 56. The deflection surface 72 provides a means for deflecting the drill bit 18 in a direction opposite the side of the bit body 56 on which the deflection surface is disposed. The deflection surface may comprise hardened steel or carbide teeth used to crush drilling spoils created by the cutting teeth 70 as the drilling spoils pass from the nose section 54 up the borehole 12 (FIG. 1).

The nose section 54 is connected to the front end of the bit body 56 and has frontwardly facing surface 60. A plurality of spaced rock cutting teeth 70 are mounted on the frontwardly facing surface 60 of the nose section 54. The rock cutting teeth 70 generally comprise a carbide tip and are mounted in the nose section 54 to rotate relative to the drill bit 18 about an elongate axis 71 of the cutting tooth. The nose section 54 also may comprise a front brow 74 at a position opposite the steering face 68. The brow 74 extends radially outward from the nose section 54. The frontwardly facing surface 60 comprises an arcuate front face of the brow 74.

The offset angle of the drill bit 18 of the present invention is illustrated in FIG. 3. FIG. 3 shows a six (6) degree angle between the second axis of rotation 62 and the first axis of rotation 58. FIG. 3 also illustrates the steering face's 3:1 rise over run and a 27.3 degree angle between the steering face 68 and the first axis of rotation 58. The six (6) degree offset shown in FIG. 3 also results in a 21.3 degree angle between the steering face 68 and the bottom of the bit body 56.

As used herein the “rise” of 3.07 inches is measured from the outermost diameter of the brow 74 (see reference numeral 76) to the first axis of rotation 58 wherein it intersects the plane of the steering face 68 (see reference numeral 78). The “run,” as used herein is defined by the distance from the frontwardly facing surface 60 to intersection point 78.

The drill bit 18 of the present invention is advantageous because it functions to increase the cutting diameter of the tool while maintaining a smaller circumference. For example, a typical 3.5 inch downhole tool cuts a 5.3 inch diameter borehole. Because the cutting teeth 70 are moved further away from the first axis of rotation 58 in the drill bit 18 of the present invention, a 4.5 inch cutting face is created that is capable of cutting a 6.4 inch borehole. An increased diameter borehole is advantageous for reducing the difficulty of backreaming through hard soil or rock.

Various modifications can be made in the design and operation of the present invention without departing from the spirit thereof. Thus, while the principal preferred construction and modes of operation of the invention have been explained in what is now considered to represent its best embodiments, which have been illustrated and described, it should be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described. 

1. A drilling bit for use in directional drilling, the bit comprising: a connector section having a first axis of rotation; a front nose section having a frontwardly facing surface; a bit body which slopes from the connector section to the front nose section; wherein the front nose section and the bit body comprise a second axis of rotation about which the front nose section and hit body are rotated; and a steering face disposed on a side of the bit body and sloped from the connector section to the front nose section and disposed at an oblique angle relative to the second axis of rotation; wherein the first axis of rotation and the second axis of rotation are angularly offset at an offset angle of between four degrees and ten degrees.
 2. The bit of claim 1 further comprising a plurality of spaced rock cutting teeth mounted on the frontwardly facing surface of the nose section.
 3. The bit of claim 1 wherein the offset angle is approximately six degrees.
 4. The bit of claim 2 wherein the plurality of spaced apart rock cutting teeth are rotatable relative to the bit body.
 5. The bit of claim 1 wherein the nose section includes an arcuate front brow at a position opposite the steering face, wherein the brow extends radially outwardly, and the frontwardly facing surface of the bit comprises an arcuate front face of the brow.
 6. The bit of claim 1 wherein the steering face comprises a rise over run ratio of between 2:1 and 4:1.
 7. The bit of claim 6 wherein the rise over run ratio is approximately three to one.
 8. The bit of claim 5 wherein the bit body comprises a deflection surface at a position opposite the brow and deflects the bit in a direction opposite the side of the bit body on which the deflection surface is disposed.
 9. The bit of claim 1 wherein the first axis of rotation is collinear with a centerline of the connector section.
 10. A horizontal directional drilling system comprising: a drive machine: a drill string connected to the drive machine and operable in response to rotation and thrust forces from the drive machine; a downhole tool assembly connected to a downhole end of the drill string, the downhole tool assembly comprises a beacon assembly and a drill bit, the drill bit comprises: a connector section having a first axis of rotation; a front nose section having a frontwardly facing surface; a bit body which slopes from the connector section to the front nose section; wherein the front nose section and the bit body comprise a second axis of rotation about which the front nose section and bit body are rotated; a steering face disposed on a side of the bit body and sloped from the connector section to the front nose section and disposed at an oblique angle relative to the second axis of rotation; and wherein the first axis of rotation and the second axis of rotation are angularly offset at an offset angle of between four degrees and ten degrees.
 11. The horizontal directional drilling system of claim 10 wherein the drill bit further comprises a plurality of spaced rock cutting teeth mounted on the frontwardly facing surface of the nose section.
 12. The horizontal directional drilling system of claim 10 wherein the offset angle is approximately six degrees.
 13. The horizontal directional drilling system of claim 10 wherein the oblique angle is acute.
 14. The horizontal directional drilling system of claim 10 wherein the nose section comprises an arcuate front brow at a position opposite the steering face, wherein the brow extends radially outwardly, and the frontwardly facing surface of the bit comprises an arcuate front face of the brow.
 15. The horizontal directional drilling system of claim 10 wherein the steering face comprises a rise over run ratio of between two to one and four to one.
 16. The horizontal directional drilling system of claim 15 wherein the rise over run ratio is approximately three to one.
 17. The horizontal directional drilling system of claim 10 comprising: a radially extending brow formed on the nose section at a position opposite the steering face; and a plurality of rock cutting teeth mounted on the frontwardly facing surface of the nose section and rotatable relative to the bit body.
 18. The horizontal directional drilling system of claim 11 wherein the rock cutting teeth comprise a cutting diameter of 6.4 inches when the bit is rotated about the first axis of rotation.
 19. The horizontal directional drilling system of claim 10 wherein the first axis of rotation is collinear with a centerline of the connector section.
 20. The bit of claim 1 wherein the oblique angle is acute. 